Heat and temper resistant alloy steel

ABSTRACT

TEMPER RESISTANT ALLOY CONSISTING ESSENTIALLY OF ABOUT: 0.15 TO 0.35% CARBON, 0.25 TO 1.0% VANADIUM, UP TO 2% EACH OF MANGANESE, SILICON AND NICKEL, UP TO 3% MOLYBDENUM, UP TO 2% CHROMIUM, UP TO 6% EACH OF TUNGSTEN AND COBALT, UP TO 0.5% OF METAL OF THE GROUP OF COLUMBIUM, TITANIUM AND TANTALUM, SAID ALLOY CONTAINING AT LEAST 1% OF METAL OF THE GROUP MOLYBDENUM AND TUNGSTEN, AND THE VANADIUM CONTENT BEING ABOUT 1.8 TO 3.0 TIMES THE CARBON CONTENT, BALANCE SUBSTANTIALLY IRON.

Aug. 17, 1971 c. R, slMcoE ETVAL 3,600,160

HEAT AND TEMPER RESISTANT ALLOY STEEL v Filed May 14, 1968 CL4/950m A@ #C 725mm @W50/y United States Patent 3,600,160 HEAT AND TEMPER RESISTANT ALLOY STEEL Charles R. Simcoe and Alvin E. Nehrenberg, Lockport,

N.Y., assignors to Wallace-Murray Corporation, New

York, N Y.

Continuation-impart of application Ser. No. 402,295, Oct. 7, 1964. This application May 14, 1968, Ser. No. 729,096

Int. Cl. C22c 39/00, 39/121 U.S. Cl. 75-1231 3 Claims ABSTRACT 0F THE DISCLOSURE Temper resistan-t alloy consisting essentially of about: 0.15 to 0.35% carbon, 0.25 to 1.0% vanadium, up to 2% each of manganese, silicon and nickel, up to 3% molybdenum, up to 2% chromium, up to 6% each of tungsten and cobalt, up to 0.5% of metal of the group of columbium, titanium and tantalum, said alloy containing at least 1% of metal of the group molybdenum and tungsten, and the vanadium content being about 1.8 to 3.0 times the carbon content, balance substantially iron.

This application is a continuation-in-part of our copending application Ser. No. 402,295, led Oct. 7, 1964, now abandoned.

This invention relates to martensitic, heat resistant alloy steels which are hardened by rst being cooled from a high or austenitizing temperature at a rate sufciently rapid to form martensite, and which undergo secondary hardening upon thereafter heating in the temperature range 900 to 1300 F., or higher to develop a useful set of properties for application at room temperature and below or at elevated temperatures up to and above the tempering temperature.

An object of the invention is to provide a medium carbon alloy steel with greater resistance to tempering than steels previously known, and such that articles made from this steel can be used to higher working temperatures than heretofore, and retain useful hardness and shape.

A further object of the invention is to provide an alloy steel of superior temper resistance with mechanical properties which are useful and necessary for hot Working dies and tools and for general high-temperature applications.

In general, this invention resides in a combination of chemical elements and proportions thereof, which influence the type of carbide particles formed during the tempering operation. The control of the carbide types provides the increased tempering resistance.

The main object of our invention is to incorporate maximum resistance to tempering, that is maintain a high hardness, in medium carbon steels which are tempered `in the temperature range 900 .to l300 F. Further, our invention permits the retention of higher hardness at temperatures of 1100 to 1300 F. where steels presently known and used temper to much lower hardness levels.

Typical of the known temper resistant steels of medium carbon content are the AISI H-ll, H-12 and H-13 or the H-21 and H-22 types. The AISI Hl1, H-l2 and H-l3 steels contain 5% Cr, 1% Si, 1.5% Mo and either 0.40% V (H-ll) or 1.0% V (H-13) or 0.40% V with 1.5% W (H-l2). H-21 contains 3.5% Cr and 9% W and H-22 contains 2% Cr and 11.5% W. When these steels are tempered at high temperatures, the 5% Cr type form the carbide Cr7C3 in addition to other carbides containing Mo and V or M0, W and V. The H-21 and H-22 steels form a carbide of the W2C type. The loss of tempered hardness at high tempering temperatures is associated with the formation of Cr7C3 and MGC carbides where M is a plurality of metals, and with the growth of the W2C, Mo2C and VC carbides.

We have discovered that certain combinations of W, Mo and V are substantially more effective in providing temper resistance than the alloys known and used at present. These combinations are such that the complex carbide MC is the principal carbide present, where C is carbon and M a plurality of metals forming carbides therewith. Also the optimum amount of alloy required is that necessary to combine with all the carbon present in the steel composition. It is further necessary that the content of Cr when present be kept low so that Cr7C3 cannot form nor Cr enter into the complex carbide, MC, or influence the growth of the carbides which provide the hardness in alloys of this type.

It is known that steels which contain only W or Mo provide secondary hardening and red hardness by the formation of the M2C type of carbide. It is also known that steels containing only V provide secondary hardening and red hardness by the formation of the VC carbide. It is further known that the VC carbide has some solubility for Mo and W. We have found that the MC type carbide which is formed by adding Mo and/or W to a steel containing V further improves the red hardness over that attainable when only V is present in the MC carbide. In fact we nd that for a 0.30% C steel the optimum temper resistance is obtained with about 0.6% V, 1.6% Mo and 2.6% W. While the proportions of carbon, W, Mo and V can be varied to some extent, there is a limit to both the minimum and maximum amounts for superior temper resistance. We have determined that increasing the W from 2.6% to 4.0% and the Mo from 1.6% to 3.1% in a steel containing 0.22% C and 0.6% V causes an extensive reduction in temper resistance. Likewise the temper resistance is lower if not enough alloy addition of the W, M0 and V series is present in relation to the carbon content. In such case the carbon which is not combined with these strong carbide formers will form the carbide FeaC, which adversely affects heat resistance.

We have further found that a denite relationship exists between the amount of V available for the MC carbide and the tempered hardness. This relationship exhibits a maximum when the ratio of the carbon present as vanadium carbide to the total carbon content of the alloy is about 0.5 as shown in the accompanying drawing. Thus, if the MC carbide predominates, the maximum tempered hardness occurs when 50% of the metal content of this carbide is V and the other 50% is W plus Mo. While the maximum hardness occurs when V content of MC carbide is 50% of the total metal, this is not the only composition of economic value. Alloys containing MC carbides wherein V represents from 40% to 70% of the metal content are all superior to present commercial die steels of the 5% Cr type. At low V contents, below about 0.25%, the M2C, M7C3 or M3C type carbides form instead of the MC type carbide. The tempered hardness then depends primarily upon other factors rather than the V content. At high V contents, more and more V is present in the MC carbide until eventually all the metal content is V.

Our principal discovery is that alloying the VC carbide with W and Mo increases the temper resistance until a maximum is obtained at an alloy balance of 50% V and 50% Mo-I-W in the MC carbide, and that superior results are obtained within the aforesaid range wherein V represents from 40% to 70% of the metal content of the MC carbide, this range being critical for purposes of the invention. The novelty of this invention further resides in two additional discoveries whch distinguish it from heretofore .existing knowledge. In the first place, all prior art temper resistant alloys depend upon a single carbide type other than MC or a combination of carbide types to provide resistance to softening at elevated temperatures, and it has not heretofore been recognized that the MC type carbide is more effective than others. Secondly, chromium is almost universally used in amounts in excess of about 2% to provide hardenability in temper resistant alloys, but we have discovered this level of chromium actually causes a deterioration in the tempering characteristics and should be minimized. The adverse effect of chromium is partially responsible for the prior art alloys being inferior to those of this invention.

In our invention we wish to prevent, or at least minimize, the formation of carbides other than MC. We do this by controlling the composition in such a way that the MC carbide predominates and V constitutes 40 to 70% of the metal content thereof. Suitable amounts of two or more of the elements M0, W, Cb, Ti and Ta are added within the broad alloy range given below to provide the balance of the required metal content of the MC carbide.

The compositional balance required to assure that MC carbide of the right composition exists is obtained by a simple calculation. The atomic weights of V and C are 5l and 12, respectively. Since these elements are present in the atomic ratio 1:1 in MC carbide, the ratio by weight is 51:12 or 4.25 :1. Therefore, for an alloy having 0.30% carbon the V required to provide 50% of the metal content is equal to Two or more of the elements Mo, W, Cb, Ti or Ta are added in sui'licient quantity to provide the remainder of the metal content of the alloy. If excessive amounts are added, MozC, W2C or (Mo, W)2C will form and the resistance to softening will decrease. Note that Cr does not enter into our calculations because we do no form CrqC3. We use this element only for the purpose of prowiding hardenability.

As above stated useful alloys according to the invention are those wherein the vanadium content of the MC carbide falls within the range of 40 to 70% of the metal content thereof. Thus employing the above basis of calculation the V:C relationship for the minimum, optimum and maximum vanadium contents in the MC carbide may be expressed in terms of the carbon content by the following equations, respectively:

Percent V min.=4.25(.40)(percent C) or (l.7)% C Percent V 50%:425' (50) (percent C) or (2.1)% C Percent V max.=4.25 (.70) (percent C) or (3.0) C

The ratio of vanadium to carbon content expressed in atomic perecnt versus weight percent is given by the following equation:

Atomic Weight 1 L C 4.25 C

As above stated the atomic percent V/C falls in accordance with the invention within the range of 40-70%. l

Broad and preferred composition ranges for steels according to this invention `are as follows:

Composition wt. percent Steel Broad range Preferred range 15e. 35 0-2. 0 0-6 0-3 0. 25-1. 0 0-2. 0 0-2. 0 0-2. 0 0-6. 0 040. 5 1 1. 0 Balance Fo 1 Min.

NOTE: V=(1.7 to 3.0) percent C.

As shown by the above tabulation, nickel, manganese and chromium are preferably added to the steel for imparting hardenability, but the chromium should be limited to less than 2% to avoid a loss in temper resistance. The carbon can be varied from as low as 0.15% to as high as 0.35% but a preferred range is 0.20 to 0.35%, with an optimum range of about 0.25 to 0.35% for the most economical use of the alloy. It is the carbon content which dictates the total alloy requirement since the carbon must be combined with W, Mo and V in an MC carbide. Also the proportions of W, Mo and V in the alloy can vary; however, there must be enough V present to establish the correct carbide type and the M0 and W must be limited to minimize the formation of MZC.

The improvement in temper resistance of our alloy steel compositions over those previously used is shown in the following Table I:

TABLE I Room Temperature Hardness (Re) After lenlpeling at Indicated Temperatures *Compositionz 0.30 C, 2.0 W, 1.6 M0, 0.6 V, 1.0 Cr, 1.5 Ni, 1.5 Mn, atomic percent V/C :0.47.

As shown in the table, experimental steel No. 9 according to this invention, has far greater temper resistance than steels H-ll, H-12, H-l3 and H-21 and slightly greater temper resistance than steel H-22. Furthermore, the alloy cost for the alloy of the invention is signicantly lower than for the high tungsten alloys and this provides an additional improvement over existing alloys. We have also discovered that the presence of 5% Cr, which is used in most hot-work die steels, is detrimental to the temper resistance of our type of steel. Table II below shows the effect on temper resistance of increasing the Cr from 1.0 to 5.0% in an 0.26% C steel. This is an observation which has heretofore generally been unrecognized by those skilled in the prior art relating to heat resistant alloys of the type falling under the scope 0f this invention.

TABLE ll The Elleet of Chromium on the Tempered Hardness (Re) Tempering temperature, F.

The advantage of the MC type carbide over Mo2C or W2C in supplying temper resistance is shown in the following Table III:

TABLE III The Effect of Carbide Type on the Tempered Hardness (Re) Tempering temperature, F.

Steel Carbide type 1,100 1, 150 1, 200 1, 250

0.23 C, 4.84 Mo, 0.92 Cr, 1.58 i, 1.1 Mn.- M020, MsC 46 37 32 29 0.21 C, 9.1 W, 1.03 Cr, 1.59 Ni, 1.5 Mn W2C, M00 47 38 35 27 0.23 C, 4.82 089V, 1.10 Or, 59 Ni, 1 51 Mn MC 50 47. 5 44 35. 5

TABLE IV e ElleThct of Excess W and M0 on the Tempered Hardness (Re) 2. A temper resistant alloy steel consisting essentially of about: 0.3% carbon, up to 2% each of nickel, chromium, manganese and silicon, up to 5% cobalt, 0.6% vanadium, 2.6% tungsten, 1.6% molybdenum, the amount of vanadium, tungsten and molybdenum providing carbides principally in the MC form, with vanadium con- Temperng temperature, F.

Steel 1, 100 1, 150 1, 200 l, 250

0.22 C, 2.6 W, 1.5 M0, 0 6V, 1.07 Cr, 1.58 Ni, 1.25 Mn 49 48 44 35 0.22 C, 4.0 W, 3.1 M0, 0.63 V, 0.94 Cr, 1.7 Ni, 1.18 Mn 50 47 31 22 The second steel containing an excess of W and Mo has less temper resistance because of the formation of (Mo, W)2C which coarsens at a lower tempering temperature and nally leads to the Aformation of MGC.

What is claimed:

1. A temper resistant alloy steel consisting essentially of about: 0.15 to 0.35% carbon, up to 2% each of manganese, silicon, nickel, and chromium, up to 6% cobalt, vanadium from 1.7 to 3 times the carbon content but within the range of 0.25 to 1.0% in combination with at least 1% of carbide forming metal of the group molybdenum and tungsten but not exceeding 3% molybdenum and 6% tungsten, and up to 0.5% of carbide forming metal of the group columbium, titanium and tantalum, said carbide forming metal being present in an amount suicient to combine with the carbon in excess of that available to form carbides in the MC form with the vanadium present in said alloy and to provide carbides principally in the MC form when the alloy is austenitized, quenched and tempered at about 1100-1300 F. wherein M comprises vanadium and the additional carbide forming metal and vanadium is 40-70% of the metal content of such carbides, and the balance iron except for impurities, said alloy being characterized by a Rockwell C hardness of about 35-55% as austenitized, quenched and tempered at about 1100-1300 F.

UNITED STATES PATENTS 2,147,123 2/1939 Emmons 75-128.85 2,327,561 8/ 1943 Russell 75-128.85 2,572,191 10/ 1951 Payson 75-126F 3,155,500 11/1964 Anthony 75--126H 3,291,655 12/ 1966 Gill 75-126E 3,316,084 4/ 1967 Manganello 75-128.85

HYLAND BIZOT, Primary Examiner U.S. Cl. X.R.

-126C, 126E, 128V, 128W 

